1. Field of the Invention
This invention relates to methods for hydrolyzing wood to provide D-(+)-xylose.
2. Description of the Prior Art
D-(+)-xylose and its hydrogenation product, xylitol, are of considerable industrial importance. For example, xylose can be employed for various purposes in the foodstuffs industry, while xylitol has proved to be a very good sweetener for diabetics.
It is known to hydrolyze deciduous wood with mineral acid, for example, hydrochloric acid or sulphuric acid, under normal pressure or under super-atmospheric pressure (compare, for example Austrian patent 266 865 and British patent 922 685). A xylose yield of only approximately 10 to 12 percent is obtained. Furthermore, the material which remains, so-called cellolignin, cannot be utilized.
The so-called saccharification of wood is also known (compare, for example, DT-PS 1 183 870, German Offenlegungsschrift 1 567 335, 1 567 350 and 1 642 534), but hitherto this method has hardly been utilized industrially. In the saccharification process, the lignin remains as a non-utilizable brown insoluble product. A further disadvantage of this process is that the acetic acid which is chemically bonded in the wood (about 6 percent) is split off during the hydrolysis of the pentosan and interferes with the neutralization of the mineral acid required for this process, so that considerable consumption of ion exchangers becomes necessary. Furthermore, materials also pass into the hydrolysis solution which interfere with the hydrogenation of the xylose to xylitol, thereby lowering the yield of the latter and requiring that a careful prior purification be carried out.
Accordingly, there is a need for a process for the hydrolysis of deciduous wood which, firstly, permits complete utilization of the starting material and, secondly, gives a higher yield of xylose, thus rendering the process economical.